..............................................TypeError: #<Class:0x0000001cd78f40> can't be coerced into BigDecimal
from (irb):4:in `**'
from (irb):4:in `block in irb_binding'
from (irb):3:in `times'
from (irb):3
from /home/tony/.rbenv/versions/1.9.3-p194/bin/irb:12:in `<main>'

(The '.'s being the debug print of the putc.) I understand the documentation says only integer powers are supported for BigDecimal, however there is code support for floats and rationals, and it should fail or work reliably either way.